Vulcanization of rubber



Patented Aug. 29, 1944 UNITED STATES PATENT OFFICE VULCANIZATION OF RUBBER Paul C. Jones and Roger A. Mathes, Akron, Ohio, assignors to The B. F. Goodrich Company, New York, N. Y., a corporation of New York No Drawing. Original application February 8,

1939, Serial No. 255,358. Divided andthis application April 4, 1942, Serial No. 437,690

8 Claims. This invention relates to the vulcanization of rubber and to rubber compositions vulcanized in" the presence of the accelerators herein described. Thls case is a division of our copending application Serial No. 255,358, filed February 8, 1939,

lent accelerators of vulcanization and which contain the structure wherein A is a fatty acid residue. This invention compounds known as 2-mercaptothiazolines, of

which the simplest member has the structural formula (i -SH H2 C S 5 1 are poor accelerators of vulcanization. This was unexpected in view of their structural similarity to the mercaptothiazoles, which are among the best accelerators known.

We have discovered, however, that mixed zinc salts of monocarboxylic acids and 2-mercaptothiazolines are excellent accelerators of vulcanization. Besides the mixed salts of Z-mercaptothiazoline itself, related compounds wherein one or more of the hydrogens onthe carbon atoms of the thiazoline nucleus are replaced by aliphatic or aromatic groups may be employed to accelerate the vulcanization of rubber. Such salts can be prepared from Z-mercapto l-methylthiazoline; 2- mercapto 5-methylthiazoline; 2-mercapto 4- phenylthiazoline; 2-mercapto 4-methoxymethylthiazoline; 2-mercapto 4-anisylthiazoline; 2mercapto 4-chlormethylthiazoline; Z-mercapto 4-(pamino) phenylthiazoline; 2-mercapto 4,4-diethylthiazoline; Z-mercapto 4,5-dimethylthiazoline; and 2-mercapto 4,5-tetramethylenethiazoline and similar compounds.

The mixed zinc salts of this invention are readily prepared from zinc oxide, a 2-mercaptothiazoline and a carboxylic acid (preferably a fatty acid). It has been found that these compounds may be reacted to form mixed zinc salts of fatty acids and 2-mercaptothiazolines which are excelis particularly advantageous because the relatively highmelting zinc salts of 2-mercaptothiazolines. are sometimes rather difilcult to disperse, while the lower-melting mixed zinc salts'of a 2- mercaptothiazoline and asaturated or unsaturated fatty acid, preferably one containing eight or more carbon atoms, have equivalent accelerating activity and are easily dispersed in rubber.

The mixed zinc salts of 2-mercaptothiazolines and'fatty acids may be prepared by reacting a fatty acid, zinc oxide and a Z-mercaptOthiazoline in a 1i 1: 1 ratio, one mole of water being split off. Thus, 8.1 parts by weight of zinc oxide, 28.4 parts of stearic acid, and 11.9 parts of 2-mercaptothiazoline are reacted by stirring and heating the melted reactants until 1.8 parts of water are given off and a homogeneous mixture is obtained. The mixed salts are in general soap-like materials which melt below 120 C., and are much more easily dispersed in rubber than the highermelting zinc salts of mercaptothiazolines. The zinc salt of Z-mercaptothiazoline, for instance, from which the foregoing accelerator was pre pared melted at about 235 0., while the mixed salt melted at about 120 C.

To demonstrate the effectiveness of the accelerators of this invention, the following compositions were prepared.

Good dispersions of all of the above accelerators in the rubber compositions were obtamed with ease.

The characteristics of the above compositions cured for varying times at 287 F. were as follows, T signifying tensile strength at break in lbs/in. and E signifying ultimate elongation in percentage:

It will be observed that all of the materials tested were good acceleratorsof-vulcanization.

Any of the saturated or unsaturated monocarboxylic acids such as caprylic, palmitic, oleic, ricinoleic, benzoic, salicylic, toluic or other like acids may be employed in place of the materials 7 used in the specific examples.

Although the use of the accelerators of this invention has been described in detail in connecg mercapmthiazonne a fatty acid tion with specific rubber compositions, it will be evident that this invention is applicable to rubber compositions of themost varied nature, and that all manner of rubber goods including pneumade and solidrubber tires, tubes, hose, belting, v packing boots and shoes-surgical rubber goods,

seamless dipped rubber articles, etc. may be vulcanized-in-the presence of the accelerators here- 'in described; The accelerator may be incorany similar process. or in the-case of latex, rubbercement, or any other natural-or artificial wdispersionor solution of rubber by simply dis- :-so1vingor suspending the acceleratortherein. r The vulcanization may be performed in other --manners than that particularly set forth in the specific examples; specifically, rubber composi- -tions may-beheated. inthe-presence of sulfur or i aselenium in hot airfsteam, hot water, etc.

- It is to be.-understood thatthe term ."a rubber -is employed in=theappendedclaims in a generic sense to designate .thosergrubbery. materials which alevulcanizable: with sulfur, including porated in the-rubber .by mastication, milling or bodiments of our invention, We do not intend to limit ourselves solely thereto, for it will be obvious to those skilled in the art that many modifications such as using other materials having equivalent properties and varying the proportions of -materials used are Within the spirit and scope of the invention as defined in the appended claims.

We claim:

1. The process which comprises vulcanizinga rubber in the presence of a mixed zinc salt of a Z-mercaptothiazoline and a monocarboxylic acid containing no functional groups other than the carboxylic group.

2. The process which comprises vulcanizing a rubber in.the presence of a'mixed zinc salt of a ,3. The-process which comprises vulcanizing a rubber in the-presence of amixed zinc salt of Z-mercaptothiazoline and a fatty acid.

4. The process which comprises vulcanizing a rubber in the presenceof a mixed zinc salt of thiazolineand a monocarboxylic acid containing no functional groups other than the carboxylic group.

6. A rubber Which has been vulcanized in the presence of a mixed zinc salt of a Z-mercaptothiazoline'and a fatty acid. 

